This application claims the priority of German Application No. 198 04 641.3, filed Feb. 6, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a distance-related cruise control system and, more particularly, to a distance-related cruise control system for motor vehicles having an electronic control unit.
A cruise control system of this type is known, for example, from U.S. Pat. No. 5,014,200. Known adaptive cruise control systems of this type, in particular, consist essentially of two components:
1. a cruise controller which basically maintains a speed defined by the driver constant; and PA1 2. a sensor system for sensing the distance to the respective vehicle driving ahead.
In the case of distance-related adaptive cruise control systems, a defined speed is basically kept constant until a defined minimum distance is achieved to the vehicle driving ahead, or until there is a falling below that defined minimum distance. When this defined minimum distance is reached or when there is a falling below this defined minimum distance, a cruise control operation takes place such that the defined minimum distance (following distance) is maintained in the form of a distance-controlled following drive.
Furthermore, distance-related cruise control systems are known which comprise an automatically distance-controlled stopping action to a complete stop behind vehicles driving ahead. In this case, an increased deceleration capability is permitted with decreasing speed values. In the following, the term "deceleration capability" signifies the maximal deceleration required by the cruise control system. However, not all vehicles can reliably keep a vehicle stopped, which was automatically stopped in this manner, by means of an automatically acting brake system. Safety-critical situations may occur in this case when a driver leaves an automatically stopped vehicle without operating a manual braking device. An automatic stopping to a complete stop may also lead a driver to assume that the adaptive cruise control system, even in critical situations as the result of braking interventions, always offers a sufficient and fully automatic aid. However, such distance-related adaptive cruise control systems should be understood as comfort systems, in which the driver should remain completely responsible as the monitoring party.
It is therefore an object of the invention to improve a distance-related cruise control system such that the driver is always aware of the operating limits of the system, and that he can experience the operating limits particularly in danger-free situations.
This object is achieved by a distance-related cruise control system for motor vehicles having an electronic control unit. By means of the control unit, in the event of a distance-controlled following travel with a defined following distance from the vehicle driving ahead, when the speed falls below a defined first threshold, in the event of a further decrease of the speed of the vehicle driving ahead, the deceleration capability is reduced independently of a maintaining of a following distance. An advantageous further development of the invention is described herein.
In contrast to the conventional approach of increasing the deceleration capability with decreasing speed values, the deceleration capability, which is normally implemented by the connection of the cruise control system with an actively controllable braking system, starting with a defined low speed value, is preferably continuously reduced to zero or to the engine drag moment with a further decreasing speed. The reduction of the deceleration capability forces the driver to intuitively take over the driving of the vehicle at low speeds.
In order for the taking-over of the driving of the vehicle to occur in time and in uncritical driving situations, preferably before initiating the reduction of the deceleration capability, the defined following distance is first increased. Preferably, the increase of the following distance takes place at an increasing negative relative speed with respect to the vehicle driving ahead.
By ensuring that the driver is fully responsible for driving the vehicle, safety is increased by means of the cruise control system according to the invention.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.